Role of Crack-Tip Residual Stresses in Stress Corrosion Behavior of Pre-stressing AA7020

Abstract

This paper analyzes stress corrosion cracking (SCC) of pre-cracked samples in the presence of compressive residual
stresses generated in the vicinity of the crack tip during fatigue pre-cracking. Research focuses on the role of cracktip
residual stresses of compressive nature, generated by fatigue loading, in stress corrosion cracking of pre-cracked
samples of medium high strength aluminum alloy 7020 subjected to localized anodic dissolution and hydrogen
assisted cracking. Fatigue pre-cracking load on the samples generates compressive residual stresses in the vicinity of
the crack tip which improve the stress corrosion behavior of the aluminum alloy by delaying either the metal
dissolution or the hydrogen entry, thus increasing the fracture load in an aggressive environment. The rice model of
the residual stress distribution in the vicinity of a crack tip may be usedto explain these retardation effects by
estimating the stress level and plastic zone size. Microscopically, compressive residual stress produce a transition
topography between the fatigue pre-crack and the cleavage-like (unstable) fracture mode.